We have cloned and sequenced a 414-bp avian neurofibromatosis 1 (aNF1) cDNA which is 82% identical to the human NF1 gene at the nucleic acid level and 93% identical at the predicted protein sequence. We have used this probe to establish the normal expression pattern of aNF1 in early chicken and quail embryos, and to examine the potential role of aNF1 in neural crest (NC) development. Northern blot analysis shows a large (12.6kb) aNF1 transcript expressed with increasing levels from day 2 to day 6 in ovo. Immunoprecipitation studies show a similar increase in the expression of NF1 protein product, neurofibromin, from day 2 to day 6 in ovo. In situ hybridization experiments show aNF1 is expressed no earlier than stage 8 (26-29 hours in ovo), with ubiquitous expression from stage 8 through stage 29 (6 days in ovo). Immunohistochemistry labels a subset of neurofibromin-positive neural crest cells at stages 13 (2 days in ovo) and 20 (3 days in ovo) and neural crest derivatives at stage 27 and 29 (5 and 6 days in ovo). To examine the role of neurofibromin in neural crest cells further, we have generated a quail neural crest cell line, sQNC-1, by infecting primary quail NC cultures with the PA101 temperature sensitive mutant of the Rous Sarcoma virus. When treated with 5x10-7M retinoic acid (RA), these cells take on a neuronal morphology: they extend long neuron-like processes, and begin to express a neuron-specific isoform of '-tubulin. Concomitant with RA- induced differentiation, we see an increase of at least ten-fold in both NF-1 message and protein levels, inviting speculation that NF1 plays a role in the differentiation of neurogenic cells in the neural crest.